1. Field of the Invention
The present invention pertains, in general, to a printed circuit board with opto-via holes and a process of forming the opto-via holes and, in particular, to a printed circuit board with opto-via holes for transmitting an optical signal to an optical waveguide in the printed circuit board, and a process of forming the opto-via holes.
2. Description of the Prior Art
As well known to those skilled in the art, a printed circuit board (PCB) functions to connect various electronic components to each other on a board along a predetermined pattern, and is applied to various electronic goods such as home appliances including a digital TV and advanced telecommunication equipments.
A conventional PCB comprises a copper plate on which a circuit pattern is formed, and an inner and an outer layer. However, recently, an electro-optical circuit board (EOCB) is frequently used instead of the conventional PCB. At this time, the EOCB is formed by inserting an optical waveguide comprising polymer and glass fiber, for transmitting and receiving an optical signal and into the PCB.
In other words, the EOCB is the PCB into which the optical waveguide and a glass plate are inserted after a circuit pattern is already formed on the PCB, and it transmits and receives both an electrical signal and an optical signal. Additionally, the EOCB functions to convert the optical signal into the electrical signal so as to store data or process signals in a component mounted on the PCB, and a very high speed data telecommunication is realized when the electrical signal is interfaced into the optical signal in the PCB.
Meanwhile, an opto-via hole acts as a medium for connecting the optical signal to an entrance of the optical waveguide component of an inner layer of the PCB, and is a kind of via hole of the PCB functioning to transmit signals in the PCB to a photodiode (PD) or vertical-cavity surface-emitting laser (hereinafter referred to as “VCSEL”) acting as a light source component located outside the PCB. When the optical waveguide is formed, there is a need to form the opto-via hole which acts as a channel for connecting the outer layer of the PCB to the inner layer of the PCB and easily transmits the optical signal from the inner layer to the outer layer.
In detail, in accordance with the recent trend of rapid increase in the use of the Internet and improvements of service quality on the internet, an amount of data to be processed and transmitted is rapidly increased, so it is necessary to expand a bandwidth and rapidly to process signals. Accordingly, it is required to use the EOCB as the medium of optical interfacing. That is to say, the electrical signal used in the conventional PCB is undesirably affected by electromagnetic susceptibility (EMS) characteristics during a high-speed switching process at a GHz band, so there remains a need to adopt optical interfacing which is not limited by the EMS characteristics.
A detailed description of the optical interfacing in the PCB will be given, below.
FIG. 1 schematically illustrates a beam coupling in the case of using a beam reflecting micro mirror in a conventional manner.
With reference to FIG. 1, an electrical signal transmitted from a processor board 2 is converted into an optical signal by a laser diode 1 in a transmitting module 3, transported via left lenses 8a, 8b, and then reflected by a left micro mirror 4a inserted into the PCB. The reflected signal is transported through the optical waveguide, reflected by a right reflecting mirror 4b, and then transported through right lenses 8c, 8d to a photo diode 6 in a receiving module 7. At this time, the optical waveguide is embedded within a low loss multimode polymer waveguide core 5a, 5b, and a waveguide clad 9 is formed on an upper and a lower part of the core. Therefore, the electrical signal transmitted from the left processor board 2 is converted into the optical signal and transported to a photo diode 6, and the optical signal is then converted into the electrical signal by the photo diode 6 and transported to a right processor board.
However, there is no commercial process by which the waveguide or glass plate is inserted into the PCB and connected to components outside the PCB, even though it has been ten years or more since the EOCB was first proposed. Additionally, a process of fabricating the PCB depends on a method of applying the optical signal to the PCB. Accordingly, it is necessary to desirably determine the procedure of forming the via hole so that the via hole is less affected by chemicals used to fabricate the PCB.
Furthermore, a conventional process of forming the PCB with opto-via holes is disadvantageous in that the optical waveguide component and the glass fiber are undesirably affected by physical and chemical stresses during a fabrication process of the PCB, thereby readily degrading the light transmissivity of the PCB, so there is a problem in forming the desired opto-via hole in accordance with different processes.